FIGURE 2.

Schematic representation of the seasonal cycle of cambial activity and tree ring formation in temperate coniferous trees. The black circle represents the solar calendar; the orange/green circle illustrates the seasonal evolution of cambial activity, while the blue and red circles illustrate the seasonal evolution of wood formation (enlargement and thickening period respectively). Wood formation critical dates are listed in the adjacent table along with their corresponding environmental cues (question marks indicate uncertain roles or missing evidence). Arrows indicate causal relationships between phenological phases. In the center, two cross sections show the cambium and the xylem of a Scot pine tree during winter (A), and spring (B).